Method to improve production of sulfur

ABSTRACT

A method of mining sulfur in a subterranean formation containing a sulfur-bearing zone and a porous zone adjacent said sulfurbearing zone comprising introducing a silicate solution into the porous zone and allowing the solution to set into a relatively firm and impermeable mass and then contacting the sulfur-bearing zone with a heated fluid whereby said impermeable mass prevents loss of heated fluid into said porous zone.

United States Patent [72] Inventors Hugh .1. Ayres [56] References Cited Duncan; UNITED STATES PATENTS Rune xmhmmm'okla'ihhn 928,036 7/1909 Frasch 299/6 Cook, New Orleans, La.

2.784.954 3/1957 llfrey.... 299/6 [2]] App]. No. 826,532 2 808 247 10/1957 Parks... 299/6 [221 Med May 3 I46 829 9/1964 Mann 166/292 x [45] Patented Nov. 30, 1971 [73] Assignee Halllbunon Com an Primary Examiner-Ernest R. Purser D n, Okl Almrne John H. Tregoning [54] 2 5 23; To IMPROVE PRODUCTION OF ABSTRACT: A method of mining sulfur in a subterranean for- 20 can 2 D mation containing a sulfur-bearing zone and a porous zone ad- "wing jacent said sulfur-bearing zone comprising introducing a sil- [52] 0.8. CI. 299/6, i ate s lution into the porous zone and allowing the solution 166/292 to set into a relatively firm and impermeable mass and then [5|] Int. Cl E2lc 41/14 contacting the sulfur-bearing zone with a heated fluid whereby [50] Field at Search 299/6; id imperm l m p en s lo s of h l fluid n Said 166/292 porous zone.

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.SUH/E METHOD TO IMPROVE PRODUCTION OF SULFUR The present invention generally relates to the Frasch system of mining sulfur. The Frasch system is old and well known in the art. Generally, sulfur is found in salt dome cap rock as crystal aggregates withinthe pores of limestone and .gypsum formations. in most cases the upper portion of the limestone formation does not contain sulfur. Sulfur is mined by the Frasch process by drilling a hole from the surface of the earth down into the sulfur formation. Normally, at least three concentric pipes are then inserted into the hole so that a'heated fluid can be delivered through the outer annulus between the first and second pipe into the sulfur-bearing zone to meltthe sulfur. Compressed air is then supplied through the central pipe and used to lift the liquid sulfur up throughthe annulus surrounding the central pipe.

The hot fluid used to heat the sulfur tends .to rise through the sulfur bearing formation into the porous zone of cap rock, which overlies the sulfur-bearing zone. The heated fluid which is diverted away through the porous zone is usually lost and its heat wasted. Because of the loss of water through the porous zone and other heat losses, it normally requires very large quantities of heated water to produce 1 ton of sulfur which is a thermal efficiency of less than 1 percent. The thermal efficiency could be greatly increased in loss of heated fluid through the porous zone could be prevented.

US. Pat. No. l,628,873 to Drachenberg, the disclosure of which is incorporated herein by reference, describes a method for attempting to prevent the escape of heated fluid through porous zones during mining of sulfur by the Frasch process.

According to the Drachenberg process, a heavy mud-laden water is pumped into the well above the point of discharge of the heated fluid in an attempt to fill the void in the upper porous zone and render the formation impervious to the passage of the heated fluid. As indicated in U.S. Pat. No. 2,808,247, the mud also fills the voids in the sulfur-bearing zone after sulfur has been removed and serves to prevent subsidence of the overlying strata or formations and to prevent collapse when sulfur is mined from the sulfur-bearing zone. However, the use of mud has not been completely effective in preventing the flow of heated fluid through the porous zone, and even when mud is used, large quantities of water per ton of sulfur may be required.

it is therefore an object of the present invention to provide a process for mining sulfur whereby the loss of heated fluid into the porous, nonsulfur-bearing zone is reduced.

It is a further object of the present invention to provide a method of sulfur recovery whereby the porous zone adjacent to the sulfur-bearing zone is sealed by the introduction of a fluid whereby loss of heated fluid through said porous zone is reduced.

It is a further object of the present invention to provide a method whereby a material is introduced into the porous rock adjacent to the sulfur-bearing formation to form an impermeable barrier in the porous rock.

These and other objects of the present invention will become clear by reference to the specification and examples which follow.

Briefly, the above objects of the invention are accomplished by introducing a silicate solution into the porous zone and allowing the solution to set into a relatively firm, impermeable mass so that when the sulfur-bearing zone is contacted with a heated fluid the impermeable mass blocks loss of the heated fluid into the porous zone.

The invention will be more readily understood from a reading of the following specifications and by reference to the accompanying drawings. FIGS. 1 and 2 are schematic cross sections of a sulfur well and the surrounding subterranean formation.

In general, the invention contemplates the introduction of a hardenable silicate solution into the porous zone immediately above the sulfur zone and allowing it to harden. Any suitable method for introduction of the silicate may be used. Indeed, it can be seen that the method of introduction may have to vary depending upon the nature of the individual well treated. The silicate may be added in a method similar to that described for addition of mud in US. Pat. No. 1,628,873 and 2,808,247. For example, if a sulfur. well has been treated so that there are perforations communicating directly with the lower portion of the porous barren zone, silicate may be introduced through those perforations without additional preparations.

A preferred method of introducing the silicate can be understood by reference to FIG. 1. ln completing a new sulfur well, a large casing, such an %-inch casing, is run into the porous barren zone and cemented with cement 2. Then, the hole is drilled into the sulfur zone. Normally, various logs are taken to determine the porosity, permeability, temperature profile, etc.,' of the formation. The temperature log may be used in determining the zone of loss. A cement designed for a temperature of at least as high as 325 F. should be selected since sulfur is normally produced at that temperature. The permeability and porosity logs will determine the location of the porous zone and the sulfur-bearing zone. For example, cores taken at various depths will clearly indicate the presence of sulfur.

A second casing 3, for example, a S-inch casing, is then run into the sulfur zone. The casing will normally have a formation packer collar 5 located immediately above the bottom end of the casing. The casing 3 is then cemented with a cement 6 capable of resisting temperatures encountered in the well, normally about 350 F. Although it is normally preferred to have the cement 6 extend into the annulus between casings l and 3, in practice the cement may not extend that high, as illustrated in the drawing.

If previously run logs, cores or experience indicates the presence of a porous zone immediately above the top of the sulfur, a solution should be introduced as follows. An acid solution as 10 percent acetic acid is spotted across the porous zone. Normally about 250 gallons of acid will be sufficient. Casing 3 is then perforated just above the sulfur zone. Preferably the perforations 7 should be located to each other over a 2-foot interval at a density of 4 shots per foot. After the perforations have been made, it may be desirable to first inject water into the formation at a pressure below that which will fracture the porous zone.

The data on the pumping rate for water is used to determine the pumping time required for the silicate and from that information the length of time the silicate must stay fluid before setting is determined.

The volume of silicate solutions being used is calculated from porosity measurements of the porous zone. It will normally be desired to fill a volume about 2 feet thick and extending half the distance between the sulfur well to be completed and the nearest offset well or nearest planned offset well plus an excess of about 50 percent or barrels if that is less. 0f course, it should be understood that even a small volume of silicate will be effective and in some instances a much larger volume may be desired in order to prevent escape of heated fluid at a greater distance from readily into the porous zone and there set into an impermeable barrier which will prevent the escape of heated fluid from the sulfur zone may be used. Normally, the silicate solution comprises a water solution of an alkali metal silicate plus a gelling agent or agents such as a solution of a gelling agent, e.g. calcium chloride.

As previously indicated, a wide variety of sodium silicates may be used although those having an Na 0:Sio, ratio of about 1:2-4 are preferred. Specially preferred materials are those aqueous sodium silicates having an Na,0:Si0- ratio of about 1:3.3 or 1:3.22. In addition to sodium, the alkali metal may be potassium, lithium, rubidium cesium and mixtures thereof.

The water solution of alkali metals and silicate will typically contain 35-45 percent alkali metal oxide-Si0 solids although excellent results may be obtained with other larger or smaller amounts of water.

A particularly preferred silicate solution for use in the present invention is that described in US. Pat. No. 2,986,572, the disclosure of which is incorporated herein by reference. That silicate solution contains an amide having the structure nun-van indicated by arrows 10. Of course, any desired method of injecting the fluid may be used as long as it provides for control of the silicate solution in perforated intervals.

After the silicate solution has been placed, tubing 8 is normally removed, the well is shut in and various pumps and lines are cleared of the silicate solution as quickly as possible.

The silicate solution is then squeezed and then perforations closed by inserting a ball plus into the tubing and introducing cement, nonnally about 35 sacks of either a latex cement or a Class A cement through the perforations. After the cement has set, the well is drilled out and can be completed according to standard practices for sulfur production.

Normally, sulfur production is accomplished as indicated in FIG. 2 and includes an insertion of two more tubings. Tubing 11 carries molten sulfur to the surface and inner tubing 12 carries compressed air which is used to air-lift the sulfur to the surface. Heated fluid is introduced into the formation through perforations 14. The heated fluid flows into the sulfur zone as indicated by arrows l4,'but is prevented from escaping into the porous zone by the silicate barrier. The heated fluid melts the sulfur which then flows through perforations l5 and into the tubing at 16 as indicated by arrows l7. Baffle l8 prevents flow of sulfur into the annulus carrying heated fluid.

It has been found that the introduction of the silicate solu tion to form a silicate barrier above the sulfur zone greatly reduces the amount of heated fluid required to produce a ton of sulfur by other methods including the mud placement method as described in the Drachenberg patent. For example, the best well in a field required 20,000 gallons of water per ton of sulfur, whereas a well in the same field required only 5,000 to 6,000 gallons of water after treated with silicate according to the present invention. Although the reason for the improvement through the use of silicate is not fully understood, it is though that the mud slurries which are introduced into the porous zone tend to bridge the void allowing the escape of heated fluid through the voids which remain open. The silicate solution does not contain large particles and thus can flow into even very small voids and form a uniform barrier to escape of the heated fluid.

The invention can be further understood by reference to the following example.

EXAMPLE 1 A sulfur well in Louisiana was treated according to the present invention as follows. A hole was drilled and an 8%- inch casing was run to 798 feet and cemented. The top of the porous zone, or cap rock, was located at 1,796 feet. Coring operations were carried out cutting conventional 3'-inch cores which indicated the presence of sulfur in the 1,861 to 1,884 foot zone. The sulfur occurred in all of the cores down to 1,994 feet. In the core for the interval form 1,994 feet to 2,015 feet the first 5 feet 9 inches of the core was dark gray limestone with moderate vugs and much barite. The sulfur content was low and the top of anhydrite was identified at 2,006 feet. The last 8 feet 10 inches of the core was dark gray to black cryptocrystalline anhydrite. A temperature survey was run and a peak temperature of 188 F. was recorded at a depth of about 1,840 feet.

A 5 -inch casing with a formation packer collar located at 1,951 feet and a sulfur screen extending below that to 1,956 feet was run and cemented with 55 sacks of cement after 20 barrels of gelled water were run to clean the hole. Two temperature surveys and a bond log which indicated that the cernent job was good were run. The well was then circulated packer was then set inside the SVz-inch casing with the bottom of the packer 3l8,feet above the perforations. A wafer injection test was run in the perforated'interval and an injection rate of 1.5 barrels per minute at a pressure of 300 p.s.i.g. was obtained. A sodium silicate solution having an Na,O:SiO, ratio of 1:322 and containing 8.4 percent solids, 1 percent metal salt and 1.93 percent of amide was injected into the perforated interval at pressures ranging from 450 to 550 p.s.i.g. The injection rate declined from 2.5 barrels per minute at the beginning of the job to 0.9 barrels per minute at the end of the job. A total of 840 barrels of solution was introduced into the formation with a total pumping time of about 12 hours.

After all of the silicate solution had been pumped, the well was shut in and the pumps and lines were flushed with fresh water. A ball was placed in the tubing and 35 sacks of latex cement were pumped. The well was then shut in and allowed to stand for 24 hours. The cement in the pipe was then drilled out and the perforations were tested to 300 p.s.i.g. Sulfur production was started and it was determined that one ton of sulfur could be obtained with 5,000 to 6,000 gallons of hot water.

It should be realized that the foregoing example is merely illustrative of the present invention and that the invention may be carried out using different types of silicate solutions, different placement techniques and of course different types of cements. Thus, it can be seen that the invention should be limited only by the scope of the claims which follow.

We claim:

1. The method of mining sulfur from subterranean formations containing a sulfur-bearing zone adjacent to a porous zone comprising the steps of:

introducing a silicate solution into the porous zone,

allowing said solution to set into a relatively firm, impermeable gel,

contacting the sulfur-containing zone with a liquid heated to a sufficient temperature to cause the sulfur to liquefy, whereby said gel blocks the loss of the heated liquid from the sulfur-containing zone into the porous zone,

allowing the heated liquid to liquefy the sulfur in the sulfurcontaining zone, and

withdrawing the liquefied sulfur from the sulfur-containing zone.

2. The method of claim 1 wherein the silicate solution is introduced into the bottom of the porous zone adjacent to the sulfur-containing zone.

3. The method of claim 1 wherein a casing is introduced into a bore hole extending from the surface of the earth into the sulfur-containing zone which is adjacent to the porous zone and the silicate solution is introduced down the casing 'and through perforations in the casing wall into the porous zone.

4. The method of claim 1 wherein the heated liquid is water heated to a sufficient temperature to melt the sulfur in the sulfur-containing zone.

5. The method of claim 4 wherein said water is introduced into the sulfur-containing zone after the silicate solution has set into a relatively firm, impermeable gel.

6. The method of claim 1 wherein the silicate solution is a water solution of a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate, rubidium silicate, cesium silicate, and mixtures thereof, and an activating material.

7. The method of claim 6 wherein the silicate solution is a water solution of sodium silicate and an activating material.

8. The method of claim 6 wherein said activating material is selected from the group consisting of divalent compounds.

9. The method of claim 6 wherein the activating material is calcium chloride.

10. The method of claim 6 wherein the activating material is an amide selected from the group consisting of formaldeyde, acetamide, propionamide, and butyramide.

11. The method of claim 6 wherein the activating material is a mixture of an amide selected from the group consisting of formaldehyde, acetamide, propionamide, butyramide, and a divalent compound.

12. The method of claim 6 wherein the ratio of Na O:SiO is from about 1.2 to about 1.4.

13. The method of claim 6 wherein the silicate solution contains from about 5 percent to about 43 percent by weight reactive ingredients.

14. The method of mining sulfur from a subterranean formation containing a sulfur-bearing zone adjacent to a porous zone comprising the steps of:

drilling a well bore from the surface of the earth and penetrating the sulfur-containing zone and the adjacent porous zone,

placing a casing in the well bore,

cementing the casing into the well bore,

placing a packer in the casing below the porous zone,

perforating the casing at the porous zone,

introducing a silicate solution into the porous zone through the perforations in the casing,

allowing said solution to set into a relatively firm, impermeable gel,

closing the perforations with cement,

drilling through the cement and packer into the sulfur-containing zone,

contacting the sulfur-containing zone with a liquid heated to a sufficient temperature to liquefy sulfur in the sulfurcontaining zone, and

withdrawing the liquefied sulfur from the sulfur-containing zone.

15. The method of claim 14 wherein the heated liquid is water.

16. The method of claim 14 wherein the silicate solution is water solution of an alkaline earth silicate and an activating agent,

17. The method of claim 16 wherein the activating material is selected from the group consisting of divalent compounds and amides.

18. The method of claim 16 wherein the silicate solution is a water solution of calcium chloride, sodium silicate and formaldehyde.

19. The method of claim 16 wherein the ratio of Na O:SiO is from about 1:2 to about 1:4.

20. The method of claim 16 wherein the silicate solution contains from about 5 percent to about 43 percent by weight reactive ingredients. 

2. The method of claim 1 wherein the silicate solution is introduced into the bottom of the porous zone adjacent to the sulfur-containing zone.
 3. The method of claim 1 wherein a casing is introduced into a bore hole extending from the surface of the earth into the sulfur-containing zone which is adjacent to the porous zone and the silicate solution is introduced down the casing and through perforations in the casing wall into the porous zone.
 4. The method of claim 1 wherein the heated liquid is water heated to a sufficient temperature to melt the sulfur in the sulfur-containing zone.
 5. The method of claim 4 wherein said water is introduced into the sulfur-containing zone after the silicate solution has set into a relatively firm, impermeable gel.
 6. The method of claim 1 wherein the silicate solution is a water solution of a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate, rubidium silicate, cesium silicate, and mixtures thereof, and an activating material.
 7. The method of claim 6 wherein the silicate solution is a water solution of sodium silicate and an activating material.
 8. The method of claim 6 wherein said activating material is selected from the group consisting of divalent compounds.
 9. The method of claim 6 wherein the activating material is calcium chloride.
 10. The method of claim 6 wherein the activating material is an amide selected from the group consisting of formaldehyde, acetamide, propionamide, and butyramide.
 11. The method of claim 6 wherein the activating material is a mixture of an amide selected from the group consisting of formaldehyde, acetamide, propionamide, butyramide, and a divalent compound.
 12. The method of claim 6 wherein the ratio of Na2O:SiO2 is from about 1.2 to about 1.4.
 13. The method of claim 6 wherein the silicate solution contains from about 5 to about 43 percent by weight reactive ingredients.
 14. The method of mining sulfur from a subterranean formation containing a sulfur-bearing zone adjacent to a porous zone comprising the steps of: drilling a well bore from the surface of the earth and penetrating the sulfur-containing zone and the adjacent porous zone, placing a casing in the well bore, cementing the casing into the well bore, placing a packer in the casing below the porous zone, perforating the casing at the porous zone, introducing a silicate solution into the porous zone through the perforations in the casing, allowing said solution to set into a relatively firm, impermeable gel, closing the perforations with cement, drilling through the cement and packer into the sulfur-containing zone, contacting the sulfur-containing zone with a liquid heated to a sufficient temperature to liquefy sulfur in the sulfur-containing zone, and withdrawing the liquefied sulfur from the sulfur-containing zone.
 15. The method of claim 14 wherein the heated liquid is water.
 16. The method of claim 14 wherein the silicate solution is a water solution of an alkaline earth silicate and an activating agent.
 17. The method of claim 16 wherein the activating material is selected from the group consisting of divalent compounds and amides.
 18. The method of claim 16 wherein the silicate solution is A water solution of calcium chloride, sodium silicate and formaldehyde.
 19. The method of claim 16 wherein the ratio of Na2O:SiO2 is from about 1:2 to about 1:4.
 20. The method of claim 16 wherein the silicate solution contains from about 5% to about 43 percent by weight reactive ingredients. 